The NXT RR type bit map is one bit per RR type present for the owner
name similar to the WKS socket bit map. The first bit represents RR
type zero (an illegal type which should not be present.) A one bit
indicates that at least one RR of that type is present for the owner
name. A zero indicates that no such RR is present. All bits not
specified because they are beyond the end of the bit map are assumed
to be zero. Note that bit 30, for NXT, will always be on so the
minimum bit map length is actually four octets. The NXT bit map
should be printed as a list of RR type mnemonics or decimal numbers
similar to the WKS RR.

The domain name may be compressed with standard DNS name compression
when being transmitted over the network. The size of the bit map can
be inferred from the RDLENGTH and the length of the next domain name.